Running hot

1988 Astro Van. 6 cyl. A/C Always well maintained, it has high mileage, but no oil leaks and performance is good. Lately the vehicle has been running hot. In the past, the temp. gauge would
read and stay right at 160. Lately, it has been bouncing and fluctuating wildly. From the 160 up to over 220. At a red light, the temp will skyrocket, unless I put the van in N and keep the engine pulsing. Last week, I got stuck in city traffic due to a festival that was bumper to bumper, and the only way to save the engine (??!!) was to turn off A/C and keep the engine revved up during stops. Moving at highway speeds, the temp drops to near what is normal. My mechanic, whom I trust...says he didn't find anything wrong or kaput. I am wondering about fan clutches or water pumps, will they start malfunctioning or is there just out and out failure? Perry
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Hello
I'd first suspect the t-stat. Also check the tension on the drive belt. 160 as being 'normal' doesn't seem right to me (too cold). 220 would be high-normal in most engines. Find out what the NOT (normal operating temp) for this engine is. Your guage/sensor may be faulty. If the engine was in trouble because of it being way too hot, you'd know it very quickly.
Hope this helps some.......
Dave S(Texas)
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Hello
I'd first suspect the t-stat. Also check the tension on the drive belt. 160 as being 'normal' doesn't seem right to me (too cold). 220 would be high-normal in most engines. Find out what the NOT (normal operating temp) for this engine is. Your guage/sensor may be faulty. If the engine was in trouble because of it being way too hot, you'd know it very quickly.
Hope this helps some.......
Dave S(Texas)
If the Astro has a 180, or 185 Thermostat, 160 at the gauge would be correct. Astro's with a 160 degree thermostat will actually over cool the engine. To the point unless your turning 3,000 RPM's you will not generate enough heat for the heater to blow warm air.
Part of this problem stems from a large radiator. Part from a V8 water pump. 251-594 (the AC Delcopart number), also is the same pump used on 5.7 & 5.0 Trucks and Vans till 1996. So you have a pump that is intended by design to flow enough coolant to keep a 350 at proper temps, on a engine with 2 less cylinders. Which means it's cycling the coolant out quicker.
Stock Astro Cooling systems can handle a V8 with out even changing the radiator. Charles
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First thing I would do is a pressure test on the radiator. If it passes, the next step is a new Thermostat. They do go out. After that is to check the fan clutch, if it passes, move on to the belt. Take it lose. This will give you a good idea if the tensioner spring is dying. Then inspect the belt. If in doubt replace it.
With the belt off rotate the water pump by hand. Check for fore & Aft play, shaft side play, as well as true. If it's not, replace the pump with a AC-Delco, or NAPA unit. Do not use a cheep pump on a 4.3 V6!
Depending on where you live, and your heat needs for the winter you can use a 180 or 185 degree Thermostat. Never use a 160 degree thermostat in an Astro Van if you want to use your heater. Charles
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My vote is water pump or fan clutch.
When your gauge reads high (like 200+), stop the engine and give the fan a whirl. If it is free and easy, your clutch fan is toast. It should only freewheel from just above cold thru to normal operating temperature.
I have read a number of posters that have had problems with or don't trust their astro clutch fan. They have replaced with no clutch or with electric fan.
Personally, I had wild fluctuations when my water pump was going, but this also affected my idle smoothness. Symptoms --may-- include weeping of coolant, noise, looseness of the shaft (side to side) to give you some tests.
Unless your belt is really loose, I don't think that is the source of your problems, but easy enuf to check to rule it out and/or change.
Of course the sender unit may be out to lunch, but unlikely. You should use the proper thermostat for your engine (I think it is 185) summer and winter. Your OE dash guage is not necessarily that accurate but should be in the right ballpark. If you are overheating, turn your A/C off and turn ON your heating system full. Don't let your temperature get too high or permanent damage/failure can occur.
Richard

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Clutch Fans may use a wee bit of power to run. Yet on something like an Astro, you will get better cooling with one. Especially at idle, where the fan will suck more air thru the shroud, then two electric fans would. Astro Radiators have a large surface area.To make an electric fan work well, you would have to have a large one, with a shroud that covered the rear of the surface area.
As for doing away with the clutch, that is a bad idea. To keep the cooling system working properly you would have to use a thin flex fan. Yet it would still have to be large. I have had issues with the blades cracking and coming apart. Which is why I do not use them except where they were OE. Charles
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